Use of nanoparticles in explosives

ABSTRACT

Explosives containing aqueous oxidizer solution, fuel, and a nanoparticle-stabilized foam sensitizer. The explosives may also further contain an emulsifier.

BACKGROUND

Water-based explosives are commonly classified into two types: emulsions and water gels or slurries. The emulsion type explosives typically have a dispersed phase of an aqueous oxidizer solution and continuous phase of an organic fuel. Water-gel and slurry types of water-based explosives typically have an organic fuel as the dispersed phase and oxidizer-saturated water as the continuous phase. Both types of water-based explosives require a sensitizer to enable detonation to occur, usually in the form of small bubbles. These bubbles may be hollow microspheres or gas bubbles. It is generally known in the explosives art that smaller bubbles and uniform distribution of these bubbles throughout the explosive provides good performance.

Small gas bubbles can be introduced into the water-based explosive either by chemical or mechanical techniques (e.g., bubbling a gas into the liquid). However, mechanically or chemically supplied gas bubbles are inherently unstable (i.e., the small bubbles coalesce and form progressively larger bubbles of gas). Such coalescence provides a less uniform distribution of gas bubbles and larger gas bubbles, both of which are detrimental to explosive performance and shelf life of the explosive.

It is also known to add a sensitizer in the form of small hollow microspheres or bubbles to the water-based explosive. Examples of such microspheres include those made of glass, water glass, organic polymer, or perlite. These hollow microspheres eliminate the problem of bubble coalescence, but at a much higher cost than gas bubbles. Moreover, during the incorporation of these hollow microbubbles into the explosive, gas is often unintentionally incorporated into the explosive, affecting explosive performance and shelf life of the explosive.

SUMMARY

In one aspect, the disclosure provides water-based explosives comprising aqueous oxidizer solution, fuel, and a nanoparticle-stabilized foam as the sensitizer. The nanoparticle-stabilized foam comprises an aqueous oxidizer solution-fuel mixture, and nanoparticles disposed in said oxidizer-fuel mixture, the nanoparticles having a median particle diameter of up to 100 nanometers (in some embodiments, up to 50 nanometers; in some embodiments, from 3 nanometers to 50 nanometers, from 3 nanometers to 20 nanometers, or even from 3 nanometers to 10 nanometers; in some embodiments, an average particle diameter from 3 nanometers to 50 nanometers, from 3 nanometers to 20 nanometers, or even from 3 nanometers to 10 nanometers).

In another aspect, the disclosure provides a method of providing a liquid (e.g., water-based) explosive having a stabilized foam sensitizer comprising incorporating nanoparticles having a median particle diameter of up to 100 nanometers (in some embodiments, up to 50 nanometers; in some embodiments, from 3 nanometers to 50 nanometers, from 3 nanometers to 20 nanometers, or even from 3 nanometers to 10 nanometers; in some embodiments, an average particle diameter from 3 nanometers to 50 nanometers, from 3 nanometers to 20 nanometers, or even from 3 nanometers to 10 nanometers) into a liquid explosive, and foaming the liquid explosive, wherein the nanoparticles are incorporated into the liquid explosive in an amount sufficient to stabilize the foamed liquid explosive.

In another aspect, the disclosure provides a water-based explosive precursor comprising an aqueous oxidizer solution, fuel, and nanoparticles having a median particle diameter up to 100 nanometers (in some embodiments, up to 50 nanometers; in some embodiments, from 3 nanometers to 50 nanometers, from 3 nanometers to 20 nanometers, or even from 3 nanometers to 10 nanometers; in some embodiments, an average particle diameter from 3 nanometers to 50 nanometers, from 3 nanometers to 20 nanometers, or even from 3 nanometers to 10 nanometers). In some embodiments, the water-based explosive precursor composition further comprises an emulsifier.

Exemplary nanoparticles include surface modified (i.e., nanoparticles that have a substance reacted to the respective surfaces thereof by at least one of covalent or acid/base bonding) (e.g., at least one of hydrophobically or hydrophilically surface-modified such that they are compatible with either an organic or aqueous continuous phase of a water-based explosive) and non-surface modified nanoparticles (i.e., nanoparticles that do not have a substance reacted to the respective surfaces thereof by at least one of covalent or acid/base bonding). In some embodiments, the nanoparticles include both surface modified nanoparticles and non-surface modified nanoparticles.

As used herein, “water-based explosive” includes explosives that are in the form of a liquid, gel, slurry, suspension, emulsion, colloid, and the like, wherein the explosive contains an oxidizer dissolved in water. The water may be the continuous phase (e.g., water-gels and slurries), or discontinuous phase in the case of emulsions.

“Sensitizer” means microbubbles of air, nitrogen, carbon dioxide, nitrogen monoxide and gaseous hydrocarbons and/or gas retained solid particles, such as hollow glass, water glass or organic microspheres or perlites or any other substance which provides density discontinuities within the explosive.

“Persistent foam” means the presence of gas voids in a composition for a period of greater than one minute after the composition has been foamed.

Some of the advantages of the explosives of the disclosure are expected to be improved explosive performance and improved shelf-life due to decreased gas bubble coalescence.

DETAILED DESCRIPTION

Water-based explosives comprise an aqueous oxidizer solution and fuel in the form of an emulsion, slurry, or gel. Examples of oxidizers that are useful in water-based explosives described herein include nitrate, chlorate, or perchlorate salts of ammonium, sodium or potassium, hydrazines, organic amides (e.g., monomethyl amine nitrate, and combinations thereof).

Examples of fuels that are useful in water-based explosives include any fuel capable of being oxidized in a water-based explosive as defined herein. Specific examples include fuel oil, diesel fuel, gasoline, kerosene, jet fuel, white oil (e.g., mineral oil, etc.) vegetable oil (corn oil, etc.), animal oil (e.g., seal oil, whale oil, etc.), alcohols, waxes, as well as solid organic and metal particles (e.g., aluminum, and the like).

The water-based explosives described herein include nanoparticle-stabilized foam. The nanoparticle-stabilized foam includes gas voids (i.e., bubbles), which are typically dispersed uniformly throughout the composition. The foam is persistent and preferably includes a cellular structure in which the gas voids are in the form of closed cells.

In some embodiments, the nanoparticles are individual, unassociated (i.e., non-aggregated) nanoparticles dispersed throughout the aqueous oxidizer solution-fuel mixture and preferably do not irreversibly associate with each other. The term “associate with” or “associating with” includes covalent bonding, hydrogen bonding, electrostatic attraction, London forces, and/or hydrophobic interactions.

The nanoparticles can be inorganic and/or organic. Examples of suitable inorganic nanoparticles include silica and metal oxide nanoparticles (e.g., zirconia, titania, ceria, alumina, iron oxide, vanadia, antimony oxide, tin oxide, alumina/silica, and combinations thereof). The nanoparticles have a median particle diameter up to 100 nanometers (in some embodiments, up to 50 nanometers; in some embodiments, from 3 nanometers to 50 nanometers, from 3 nanometers to 20 nanometers, or even from 3 nanometers to 10 nanometers). If the nanoparticles are aggregated, the maximum cross sectional dimension of the aggregated particle is within any of these specified ranges.

The nanoparticles may be in the form of a colloidal dispersion. Examples of useful commercially available non-modified silica nano-sized colloidal silicas (as colloidal silica) include those under the trade designations “NALCO 1040,” “NALCO 1050,” “NALCO 1060,” “NALCO 2326,” “NALCO 2327,” and “NALCO 2329”, from Nalco Chemical Co., Naperville, Ill.

Useful metal oxide colloidal dispersions include colloidal zirconium oxide, suitable examples of which are described in U.S. Pat. No. 5,037,579 (Matchett) (the disclosure of which is incorporated herein by reference), and colloidal titanium oxide, useful examples of which are described, for example, in PCT Publication No. WO 00/06495 entitled, “Nanosize Metal Oxide Particles for Producing Transparent Metal Oxide Colloids and Ceramers,” (Arney et al.), filed Jul. 30, 1998, the disclosure of which is incorporated herein by reference.

Exemplary organic nanoparticles also include buckminsterfullerenes (fullerenes), dendrimers, branched and hyperbranched “star” polymers such as 4, 6, or 8 armed polyethylene oxide (available, for example, from Aldrich Chemical Company, Milwaukee, Wis. or Shearwater Corporation, Huntsville, Ala.) whose surface has been chemically modified. Specific examples of fullerenes include C₆₀, C₇₀, C₈₂, and C₈₄. Specific examples of dendrimers include polyamidoamine (PAMAM) dendrimers of Generations 2 through 10 (G2-G10), available also, for example, from Aldrich Chemical Company. Other organic nanoparticle materials include organic polymeric nanospheres, insoluble sugars such as lactose, trehalose, glucose or sucrose, and insoluble amino acids. In some embodiment, another class of organic polymeric nanospheres includes nanospheres that comprise polystyrene, such as those available from Bangs Laboratories, Inc. of Fishers, Ind. as powders or dispersions). Such organic polymeric nanospheres will generally have average particle sizes ranging from 10 nanometers to up to 60 nanometers.

The nanoparticles are selected such that the composition formed therewith is free from a degree of particle agglomeration or aggregation that would interfere with the desired properties of the composition including the ability of the composition to foam. The nanoparticles are selected to be compatible with the aqueous oxidizer solution-fuel mixture to be foamed. For aqueous oxidizer solution-fuel mixtures that include a variety of components, the nanoparticles may be selected to be compatible with at least one component of the aqueous oxidizer solution-fuel mixture.

One method of assessing the compatibility of the nanoparticles with the aqueous oxidizer solution-fuel mixture includes determining whether the resulting composition forms a persistent foam when a foaming agent is introduced into the composition. For transparent aqueous oxidizer solution-fuel mixtures, one useful method of assessing the compatibility of the nanoparticles with the transparent aqueous oxidizer solution-fuel mixture includes combining the nanoparticles and the aqueous oxidizer solution-fuel mixture and observing whether the nanoparticles appear to dissolve in the aqueous oxidizer solution-fuel mixture such that the resulting composition is transparent. The nature of the inorganic particle component of the particle will prevent the particle from actually dissolving in the aqueous oxidizer solution-fuel mixture (i.e., the nanoparticles will be dispersed in the aqueous oxidizer solution-fuel mixture), however, the compatibility of the nanoparticles with the aqueous oxidizer solution-fuel mixture will give the nanoparticles the appearance of dissolving in the aqueous oxidizer solution-fuel mixture. As the size of the nanoparticles increases, the haziness of the aqueous oxidizer solution-fuel mixture generally increases. In some embodiments, nanoparticles are selected such that they do not settle out of the aqueous oxidizer solution-fuel mixture. In some embodiments, the further step in assessing the compatibility of the aqueous oxidizer solution-fuel mixture and the nanoparticles includes determining whether, upon subsequent introduction of a foaming agent, the composition foams.

In some embodiments, the nanoparticles include surface-modified nanoparticles. The surface-modified nanoparticles have surface groups that modify the solubility characteristics of the nanoparticles. The surface groups are selected to render the particle compatible with the aqueous oxidizer solution-fuel mixture (e.g., a component of the aqueous oxidizer solution-fuel mixture), in which the particle is disposed such that the resulting composition, upon foaming, forms a persistent foam.

Suitable surface groups can also be selected based upon the solubility parameter of the surface group and the aqueous oxidizer solution-fuel mixture. In some embodiments the surface group, or the agent from which the surface group is a reaction product of, has a solubility parameter similar to the solubility parameter of the aqueous oxidizer solution-fuel mixture to be foamed. When the aqueous oxidizer solution-fuel mixture to be foamed is hydrophobic, for example, one skilled in the art can select from among various hydrophobic surface groups to achieve a surface-modified particle that is compatible with the hydrophobic aqueous oxidizer solution-fuel mixture. Similarly, when the aqueous oxidizer solution-fuel mixture to be foamed is hydrophilic, one skilled in the art can select from hydrophilic surface groups. The particle can also include at least two different surface groups that combine to provide a particle having a solubility parameter that is similar to the solubility parameter of the aqueous oxidizer solution-fuel mixture.

The surface groups may be selected to provide a statistically averaged, randomly surface-modified particle.

The surface groups are present on the surface of the particle in an amount sufficient to provide surface-modified nanoparticles that are capable of being subsequently dispersed in the aqueous oxidizer solution-fuel mixture without aggregation. The surface groups in some embodiments are present in an amount sufficient to form a monolayer, preferably a continuous monolayer, on the surface of the particle.

Surface modifying groups may be a reaction product of a surface modifying agent. Schematically, surface modifying agents can be represented by the formula A-B, where the A group is capable of attaching to the surface of the particle and the B group is a compatibilizing group that may be reactive or non-reactive with a component of the composition. Compatibilizing groups can be selected to render the particle relatively more hydrophilic or hydrophobic.

Suitable classes of surface-modifying agents include silanes, organic acids, organic bases, and alcohols.

Particularly useful surface-modifying agents include silanes. Examples of useful silanes include organosilanes including alkylchlorosilanes; alkoxysilanes (e.g., methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, i-propyltrimethoxysilane, i-propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, n-octyltriethoxysilane, phenyltriethoxysilane, polytriethoxysilane, vinyltrimethoxysilane, vinyldimethylethoxysilane, vinylmethyldiacetoxysilane, vinylmethyldiethoxysilane, vinyltriacetoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltrimethoxysilane, vinyltriphenoxysilane, vinyltri(t-butoxy)silane, vinyltris(isobutoxy)silane, vinyltris(isopropenoxy)silane, vinyltris(2-methoxyethoxy)silane, and isooctyltrimethoxy-silane); trialkoxyarylsilanes; N-(3-triethoxysilylpropyl) methoxyethoxyethoxy ethyl carbamate; silane functional (meth)acrylates (e.g., 3-(methacryloyloxy)propyltrimethoxysilane), 3-acryloyloxypropyltrimethoxysilane, 3-(methacryloyloxy)propyltriethoxysilane, 3-(methacryloyloxy)propylmethyldimethoxysilane, 3-(acryloyloxypropyl)methyldimethoxysilane, 3-(methacryloyloxy)methyltriethoxysilane, 3-(methacryloyloxy)methyltrimethoxysilane, 3-(methacryloyloxy)propyldimethylethoxysilane, 3-(methacryloyloxy)propenyltrimethoxysilane, and 3-(methacryloyloxy)propyltrimethoxysilane); polydialkylsiloxanes (e.g., polydimethylsiloxane); arylsilanes (e.g., substituted and unsubstituted arylsilanes); alkylsilanes (e.g., substituted and unsubstituted alkyl silanes (e.g., methoxy and hydroxy substituted alkyl silanes)); and combinations thereof.

Methods of surface-modifying silica using silane functional (meth)acrylates are described, for example, in U.S. Pat. Nos. 4,491,508 (Olsen et al.), 4,455,205 (Olsen et al.), 4,478,876 (Chung), 4,486,504 (Chung), and 5,258,225 (Katsamberis), the disclosures of which are incorporated herein by reference.

Useful surface-modified silica nanoparticles include silica nanoparticles surface-modified with silane surface modifying agents (e.g., acryloyloxypropyl trimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, n-octyltrimethoxysilane, isooctyltrimethoxysilane, and combinations thereof). Silica nanoparticles can be treated with a number of surface modifying agents (e.g., alcohol, organosilane (e.g., alkyltrichlorosilanes, trialkoxyarylsilanes, trialkoxy(alkyl)silanes, and combinations thereof), organotitanates, and mixtures thereof).

Useful organic acid surface-modifying agents (e.g., oxyacids of carbon (e.g., carboxylic acid), sulfur and phosphorus, and combinations thereof).

Representative examples of polar surface-modifying agents having carboxylic acid functionality include CH₃O(CH₂CH₂O)₂CH₂COOH (hereafter MEEAA) and 2-(2-methoxyethoxy)acetic acid having the chemical structure CH₃OCH₂CH₂OCH₂COOH (hereafter MEAA) and mono(polyethylene glycol) succinate.

Representative examples of non-polar surface-modifying agents having carboxylic acid functionality include octanoic acid, dodecanoic acid, and oleic acid.

Examples of suitable phosphorus containing acids include phosphonic acids (e.g., octylphosphonic acid, laurylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, and octadecylphosphonic acid).

Useful organic base surface-modifying agents include alkylamines (e.g., octylamine, decylamine, dodecylamine, and octadecylamine).

Examples of other useful non-silane surface modifying agents include acrylic acid, methacrylic acid, beta-carboxyethyl acrylate, mono-2-(methacryloyloxyethyl) succinate, and combinations thereof. A useful surface modifying agent that imparts both polar character and reactivity to the nanoparticles is mono(methacryloyloxypolyethyleneglycol) succinate.

Examples of suitable surface-modifying alcohols include aliphatic alcohols (e.g., octadecyl, dodecyl, lauryl and furfuryl alcohol), alicyclic alcohols (e.g., cyclohexanol), and aromatic alcohols (e.g., phenol and benzyl alcohol), and combinations thereof.

A variety of methods are available for modifying the surface of nanoparticles (e.g., adding a surface modifying agent to nanoparticles (e.g., in the form of a powder or a colloidal dispersion) and allowing the surface modifying agent to react with the nanoparticles). Other useful surface modification processes are described in, for example, U.S. Pat. Nos. 2,801,185 (Iler) and 4,522,958 (Das et al.), the disclosures of which are incorporated herein by reference.

Useful surface-modified zirconia nanoparticles include a combination of oleic acid and acrylic acid adsorbed onto the surface of the particle.

In addition to stabilizing foam within the explosives described herein, the nanoparticles can also function as an emulsion stabilizer (i.e., no additional emulsifier is required).

In some embodiment, explosive precursor compositions described herein comprise aqueous oxidizer solution, fuel, nanoparticles, and emulsifier. Emulsifier is added to create an emulsion of a supersaturated aqueous solution of aqueous oxidizer solution salt(s) into the fuel phase. Useful emulsifiers include sorbitol esters, stearates, derivatives of polyisobutylene anhydrides, and combinations thereof. Useful emulsifiers are also described in U.S. Pat. No. 4,594,118 (Curtin et al.) (the disclosure of which is incorporated herein by reference) for the description of emulsifiers.

Generally, emulsifiers can be used in the explosive precursor compositions in an amount of from typically 0.5%-2.5% by weight.

Various methods may be employed to combine the nanoparticles and the aqueous oxidizer solution-fuel mixture. In one method, a colloidal dispersion of nanoparticles and fuel mixture are combined. Then the nanoparticle-fuel mixture is blended with the aqueous oxidizer solution. Optionally, for some colloidal dispersions (e.g., aqueous colloidal dispersions) prior to addition of the aqueous oxidizer solution-fuel mixture, a cosolvent (e.g., methoxy-2-propanol or N-methylpyrrolidone) may be added to the colloidal dispersion to assist removal of water. After the aqueous oxidizer solution-fuel mixture is added, the water and cosolvent are removed.

Another method for incorporating colloidal dispersions of nanoparticles into an aqueous oxidizer solution-fuel mixture includes drying the colloidal dispersion of nanoparticles to a powder, followed by addition of the aqueous oxidizer solution-fuel mixture or at least one component of the aqueous oxidizer solution-fuel mixture into which the nanoparticles are to be dispersed. The drying step may be accomplished by conventional means such as oven drying or spray drying. The surface-modified nanoparticles preferably have a sufficient amount of surface groups to prevent irreversible agglomeration or irreversible aggregation upon drying. The drying time and the drying temperature is preferably minimized for nanoparticles having less than 100% surface coverage.

Colloidal dispersions of nanoparticles can be added to the aqueous oxidizer solution-fuel mixture in amounts sufficient to provide a composition capable of foaming, preferably in amounts sufficient to provide a composition capable of forming a persistent foam.

Nanoparticles may be present in the aqueous oxidizer solution-fuel mixture in varying amounts (e.g., from about 0.01% by dry weight to about 30% by dry weight, in some embodiments, from about 0.01% by dry weight to about 10% by dry weight, and from about 0.01% by dry weight to about 5% by dry weight based on the total weight of the composition). It is to be understood that the ranges of amounts of nanoparticles also include any whole or fractional amount between 0.01 and 30 dry weight percent. In some embodiments, the nanoparticles are dispersed throughout the aqueous oxidizer solution-fuel mixture (in some embodiments, dispersed homogeneously throughout the aqueous oxidizer solution-fuel mixture).

A cosolvent can be added to the composition to improve the compatibility (e.g., solubility or miscibility) of the surface modifying agent and the nanoparticles with the other components of the composition.

In some embodiments, the composition is foamed after the nanoparticles have become dispersed throughout the aqueous oxidizer solution-fuel mixture (in some embodiments, after the nanoparticles are homogeneously dispersed throughout the aqueous oxidizer solution-fuel mixture).

The composition is foamed by forming gas voids in the composition using a variety of mechanisms (e.g., mechanical mechanisms, chemical mechanisms, and combinations thereof).

Useful mechanical foaming mechanisms (e.g., agitating (e.g., shaking, stirring, or whipping) the composition, injecting gas into the composition (e.g., inserting a nozzle beneath the surface of the composition and blowing gas into the composition), and combinations thereof).

Useful chemical foaming mechanisms (e.g., producing gas in situ through a chemical reaction, decomposition of a component of the composition (e.g., a component that liberates gas upon thermal decomposition), evaporating a component of the composition (e.g., a liquid gas, volatilizing a gas in the composition by decreasing the pressure on the composition or heating the composition), and combinations thereof).

In principle, any foaming agent may be used to foam the composition (e.g., chemical foaming agents and physical foaming agents (e.g., inorganic and organic foaming agents).

Examples of chemical foaming agents include water and azo-, carbonate- and hydrazide-based molecules (e.g., 4,4′-oxybis (benzenesulfonyl)hydrazide, 4,4′-oxybenzenesulfonyl semicarbazide, azodicarbonamide, p-toluenesulfonyl semicarbazide, barium azodicarboxylate, azodiisobutyronitrile, benzenesulfonhydrazide, trihydrazinotriazine, metal salts of azodicarboxylic acids, oxalic acid hydrazide, hydrazocarboxylates, diphenyloxide-4,4′-disulphohydrazide, tetrazole compounds, sodium bicarbonate, ammonium bicarbonate, preparations of carbonate compounds and polycarbonic acids, mixtures of citric acid and sodium bicarbonate, N,N′-dimethyl-N,N′-dinitroso-terephthalamide, N,N′-dinitrosopentamethylenetetramine, and combinations thereof.)

Suitable inorganic physical foaming agents include nitrogen, argon, oxygen, water, air, helium, sulfur hexafluoride, and combinations thereof Additionally, inorganic chemical foaming agents such as sodium nitrite either alone or with promoters such as sodium thiocyanate, ethanolamine nitrate, acrylamide, and urea may be used.

Useful organic physical foaming agents include carbon dioxide, aliphatic hydrocarbons, aliphatic alcohols, aliphatic ethers, fully and partially halogenated aliphatic hydrocarbons, and combinations thereof. Examples of suitable aliphatic hydrocarbon foaming agents include members of the alkane series of hydrocarbons (e.g., methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, and blends thereof). Useful aliphatic alcohols (e.g., methanol, ethanol, n-propanol, and isopropanol, and combinations thereof). Useful aliphatic ethers include dimethylether. Suitable fully and partially halogenated aliphatic hydrocarbons (e.g., fluorocarbons, chlorocarbons, and chlorofluorocarbons, and combinations thereof).

Examples of fluorocarbon foaming agents include methyl fluoride, perfluoromethane, ethyl fluoride, 1,1-difluoroethane (HFC-152a), fluoroethane (HFC-161), 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,2,2 tetrafluoroethane (HFC-134), 1,1,1,3,3-pentafluoropropane, pentafluoroethane (HFC-125), difluoromethane (HFC-32), perfluoroethane, 2,2-difluoropropane, 1,1,1-trifluoropropane, perfluoropropane, dichloropropane, difluoropropane, perfluorobutane, perfluorocyclobutane, and combinations thereof.

The foaming agents may be used as single components, in mixtures and in combinations thereof. The foaming agent is added to the composition in an amount sufficient to achieve a desired foam density.

The aqueous oxidizer solution-fuel mixture may also include a nucleating agent. A nucleating agent can be any conventional nucleating agent. The amount of nucleating agent to be added depends upon the desired cell size, the selected foaming agent, and the density of the aqueous oxidizer solution-fuel mixture. Examples of inorganic nucleating agents in small particulate form include clay, talc, fumed silica, precipitated silica, and diatomaceous earth. Organic nucleating agents can decompose or react at a given temperature.

One example of an organic nucleating agent is a combination of an alkali metal salt of a polycarboxylic acid with a carbonate or bicarbonate. Examples of useful alkali metal salts of a polycarboxylic acid include the monosodium salt of 2,3-dihydroxy-butanedioic acid (i.e., sodium hydrogen tartrate), the monopotassium salt of butanedioic acid (i.e., potassium hydrogen succinate), the trisodium and tripotassium salts of 2-hydroxy-1,2,3-propanetricarboxylic acid (i.e., sodium and potassium citrate, respectively), and the disodium salt of ethanedioic acid (i.e., sodium oxalate), and polycarboxylic acid such as 2-hydroxy-1,2,3-propanetricarboxylic acid, and combinations thereof. Examples of carbonate and bicarbonate include sodium carbonate, sodium bicarbonate, potassium bicarbonate, potassium carbonate and calcium carbonate, and combinations thereof. One contemplated combination is a monoalkali metal salt of a polycarboxylic acid, such as monosodium citrate or monosodium tartrate, with a carbonate or bicarbonate. It is contemplated that mixtures of different nucleating agents may be added to the aqueous oxidizer solution-fuel mixture. Other useful nucleating agents include a stoichiometric mixture of citric acid and sodium bicarbonate.

The disclosure will now be described further by way of the following Examples. All parts, ratios, percents and amounts stated in the Examples are by weight unless otherwise specified.

EXAMPLES

Heptamethyl(2-[tris(2-methoxyethoxy)silyl]ethyl)trisiloxane Coupling Agent (“Silane Coupling Agent A”) was prepared by combining 25.20 grams of tris(2-methoxyethoxy)vinylsilane (obtained from Sigma-Aldrich, Milwaukee, Wis.) and 20.00 grams of heptamethyldisiloxane (obtained from Gelest, Inc., Tullytown, Pa.) with mixing in heptane (30 grams). One drop of a platinum(0) divinyltetramethyldisiloxane catalyst (prepared as described in Example 1 of U.S. Pat. No. 3,814,730 (Karstedt), the disclosure of which is incorporated herein by reference) was added to 0.3 gram of heptane to form a solution. One-tenth gram of this solution was added to the above reaction mixture, which was then allowed to stir in a nitrogen atmosphere, without heating, overnight. The reaction continued until completion as determined by the disappearance of the Si—H peak using infrared spectroscopy (IR). Heptane was removed from the composition by evaporation under reduced pressure to give “Silane Coupling Agent A”:

(CH₃OCH₂CH₂O)₃SiCH₂CH₂Si(CH₃)₂OSi(CH₃)₂OSi(CH₃)₃.

220 grams of colloidal silica (15% by weight solids ammonia stabilized colloidal silica having an average particle size of 5 nm and a surface area of about 600 m²/g, obtained from Nalco Chemical Co., Naperville, Ill. under the trade designation “NALCO 2326”), 37.38 grams of Silane Coupling Agent A, and 388 grams of 1-methoxy-2-propanol (obtained from Sigma-Aldrich) were combined with mixing in a 4-liter glass jar. The jar containing the mixture was sealed, placed in a vented oven, and heated overnight at 80° C. The mixture was then transferred to an evaporating dish for drying and dried in a flow-through oven at 150° C. to produce a white particulate solid (“Material I”).

100 grams of colloidal silica (“NALCO 2326”) was weighed into a 500 ml round bottom 3-neck flask, equipped with a mechanical stirrer and a reflux condenser. A solution of 18.6 grams of a polyethyleneglycol-silane (obtained under the trade designation “SILQUEST A1230” from OSi Specialties, Greenwich, Conn.), and 50 grams of 1-methoxy-2-propanol (obtained from Sigma-Aldrich) was prepared separately in a beaker. The polyethyleneglycol-silane (“SILQUEST A1230”)/methoxypropanol solution was added into the flask via the open port with stirring. The beaker was rinsed with an additional amount of methoxypropanol (52.5 grams), which was subsequently added to the stirred mixture. After complete addition, the open port in the flask was stoppered and the flask placed in an oil bath. The oil bath was then heated to 80° C. and the reaction allowed to proceed for 16.5 hours. The solvents were removed in a flow through oven at 90° C. A viscous yellow liquid was recovered (“Material II”).

A surface-modified nanoparticle dispersion (5 nm size, isooctyl/methyl surface modified) was prepared using the method described in U.S. Pat. No. 6,586,483 (Kolb et al.), under the heading “Preparation of isooctyl Surface Modified Silica Nanoparticles” (the disclosure of which is incorporated herein by reference) and were dried in an oven at 150° C. to remove solvent (“Material III”).

Foaming Tests

One gram of a 0.5 weight percent solution of Material I in a biodegradable hydrogenated oil (obtained under the trade designation “VASSA LP90” from Vassa, Caracas Venezuela) produced a foam head when shaken, which was persistent.

One gram of a 0.5 weight percent solution of Material III in a biodegradable hydrogenated oil (obtained under the trade designation “VASSA LP90” from Vassa, Caracas Venezuela) produced a foam head when shaken, which was persistent.

A sample of a biodegradable hydrogenated oil (alone) (“VASSA LP90”) did not produce a foam when shaken.

One gram of a 0.5 weight percent solution of Material II in water produced a foam head when shaken, which was persistent.

A sample of water alone did not produce a foam when shaken.

0.5 gram of a 0.5 weight percent solution of Material II in water was combined with 0.5 gram of 0.5 weight percent solution of Material III in a biodegradable hydrogenated oil (alone) (“VASSA LP90”) and shaken. A stable emulsion was formed.

When 0.5 gram of water and 0.5 gram of a biodegradable hydrogenated oil (alone) (“VASSA LP90”) were mixed and shaken, the phases separated immediately.

Water Phase Preparation (Prophetic Example):

An aqueous solution of ammonium nitrate can be prepared by charging a stainless steel beaker with ammonium nitrate (7550 parts by weight)(available from Sigma-Aldrich), thiourea (10 parts by weight)(available from Sigma-Aldrich), sodium acetate trihydrate (35 parts by weight)(available from Sigma-Aldrich) and water (1905 parts by weight). The stirred mixture can be heated to 70° C. and nitric acid (available from Sigma-Aldrich, Milwaukee, Wis.) added to adjust the pH of the composition to approximately 4.3 to provide a Water Phase.

Oil Phase Preparation (Prophetic Example):

Material III can be can be added with stirring, into #2 fuel oil (380 parts by weight; available from Exxon Mobil Corp, Fairfax, Va.) and sorbitan mono-oleate (100 parts by weight; available from BASF, mount Olive, N.J.). The mixture can be stirred until the nanoparticles are uniformly dispersed and the #2 fuel oil is clear to provide an Oil Phase.

Ammonium Nitrate Fuel Oil Emulsion Preparation (Prophetic Example):

The Water Phase (at 70° C.) can be slowly added to a rapidly stirred blend of the Oil Phase (at 20° C.) and further stirred for 1 minute. To the ensuing emulsion sodium nitrite (20 parts by weight of a 1:2 sodium nitrite to water solution) can be added, and with stirring continuing for 10 seconds. The density of the final emulsion can be in the range from 1.05 to 1.25 g/ml. The fuel to oxidizer weight ratio of the emulsion would be 96.2 to 4.8, although a more typical desired ratio would be 94.5 to 5.5.

Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows. 

1. A water-based explosive comprising: aqueous oxidizer solution; fuel; and a nanoparticle-stabilized foam sensitizer, the nanoparticles having a median particle diameter up to 100 nanometers.
 2. The water-based explosive according to claim 1, wherein the nanoparticles are hydrophilic.
 3. The water-based explosive according to claim 1, wherein the nanoparticles are present in an amount of at least 0.01 dry weight percent.
 4. The water-based explosive according to claim 1, wherein the nanoparticles have a median particle diameter of up to 50 nanometers.
 5. The water-based explosive according to claim 1, wherein the nanoparticles have surface groups made from at least one of a silane, an organic acid, or an organic base.
 6. The water-based explosive according to claim 1, further comprising an emulsifier.
 7. The water-based explosive according to claim 1, wherein the nanoparticles include surface-modified nanoparticles.
 8. A water-based explosive precursor comprising: aqueous oxidizer solution; fuel; and nanoparticles having a median particle diameter up to 100 nanometers.
 9. The water-based explosive precursor according to claim 8, wherein the nanoparticles include surface-modified nanoparticles.
 10. A method of providing a liquid explosive having a stabilized foam sensitizer comprising: incorporating nanoparticles having a median particle diameter up to 100 nanometers into a liquid explosive; and foaming the liquid explosive, wherein the nanoparticles are incorporated into the liquid explosive in an amount sufficient to stabilize the foamed liquid explosive. 